Inter-cervical facet implant and method

ABSTRACT

Systems and method in accordance with the embodiments of the present invention can include an implant for positioning within a cervical facet joint for distracting the cervical spine, thereby increasing the area of the canals and openings through which the spinal cord and nerves must pass, and decreasing pressure on the spinal cord and/or nerve roots. The implant can be inserted laterally or posteriorly.

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Application,entitled, INTER-CERVICAL FACET IMPLANT AND METHOD filed Dec. 13,2004,Ser. No. 60/635,453 [Our Reference No. KLYC-01118US0], which isincorporated herein by reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. application Ser. No. ______,entitled INTER-CERVICAL FACET IMPLANT AND METHOD, filed ______ [OurReference No. KLYC-01118US2]; U.S. application Ser. No. ______, entitledINTER-CERVICAL FACET IMPLANT AND METHOD, filed ______ [Our Reference No.KLYC-01118US3]; and U.S. application Ser. No. ______, entitledINTER-CERVICAL FACET IMPLANT AND METHOD, filed ______ [Our Reference No.KLYC-01122US0] which are each incorporated herein in full, by reference.

TECHNICAL FIELD

This invention relates to interspinous process implants.

BACKGROUND OF THE INVENTION

The spinal column is a bio-mechanical structure composed primarily ofligaments, muscles, vertebrae and intervertebral disks. Thebio-mechanical functions of the spine include: (1) support of the body,which involves the transfer of the weight and the bending movements ofthe head, trunk and arms to the pelvis and legs, (2) complexphysiological motion between these parts, and (3) protection of thespinal cord and the nerve roots.

As the present society ages, it is anticipated that there will be anincrease in adverse spinal conditions which are characteristic of olderpeople. By way of example only, with aging comes an increase in spinalstenosis (including, but not limited to, central canal and lateralstenosis), and facet arthropathy. Spinal stenosis results in a reductionforaminal area (i.e., the available space for the passage of nerves andblood vessels) which compresses the cervical nerve roots and causesradicular pain. Humpreys, S. C. et al., Flexion and traction effect onC5-C6foraminal space, Arch. Phys. Med. Rehabil., vol. 79 at 1105(September 1998). Another symptom of spinal stenosis is myelopathy,which results in neck pain and muscle weakness. Id. Extension andipsilateral rotation of the neck further reduces the foraminal area andcontributes to pain, nerve root compression, and neural injury. Id.;Yoo, J. U. et al., Effect of cervical spine motion on the neuroforaminaldimensions of human cervical spine, Spine, vol. 17 at 1131 (Nov. 10,1992). In contrast, neck flexion increases the foraminal area. Humpreys,S. C. et al., supra, at 1105.

In particular, cervical radiculopathy secondary to disc herniation andcervical spondylotic foraminal stenosis typically affects patients intheir fourth and fifth decade, and has an annual incidence rate of 83.2per 100,000 people (based on 1994 information). Cervical radiculopathyis typically treated surgically with either an anterior cervicaldiscectomy and fusion (“ACDF”) or posterior laminoforaminotomy (“PLD”),with or without facetectomy. ACDF is the most commonly performedsurgical procedure for cervical radiculopathy, as it has been shown toincrease significantly the foramina dimensions when compared to a PLF.

It is desirable to eliminate the need for major surgery for allindividuals, and in particular, for the elderly. Accordingly, a needexists to develop spine implants that alleviate pain caused by spinalstenosis and other such conditions caused by damage to, or degenerationof, the cervical spine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lateral view of two adjacent cervical vertebrae andspinous processes, highlighting the cervical facet joint.

FIG. 2 depicts a lateral view of the cervical spine with spinalstenosis.

FIG. 3A depicts correction of cervical stenosis or other ailment with awedge-shaped embodiment of the implant of the invention positioned inthe cervical facet joint.

FIG. 3B depicts correction of cervical kyphosis or loss of lordosis witha wedge-shaped embodiment of the invention with the wedge positioned inthe opposite direction as that depicted in FIG. 3A.

FIG. 4 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention including a screwfixation device for attaching to a single vertebra.

FIG. 5 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising screwfixation of two implants, one implant fixed to each of two adjacentvertebrae.

FIG. 6 shows cervical spine kyphosis, or loss of lordosis.

FIG. 7 shows correction of cervical kyphosis, or loss of lordosis, witha further embodiment of the implant of the invention comprising twofacet implants with screw fixation.

FIG. 8 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant and a keel.

FIG. 9 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising facetimplant, a keel, and screw fixation.

FIG. 10 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant with teeth.

FIG. 11 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant with teeth and screw fixation.

FIG. 12 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces.

FIG. 13 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces and posterior alignment guide.

FIG. 14 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants with increased facet joint contact surfaces.

FIG. 15 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces and screw fixation.

FIG. 16 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants with articular inner surfaces.

FIG. 17 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetjoint implant with a roller.

FIG. 18 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetjoint implant with a plurality of rollers.

FIG. 19 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and elastic restraint.

FIG. 20 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and spring restraint.

FIG. 21 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and magnetic restraint.

FIG. 22A shows a perspective view of a further embodiment of implant ofthe invention.

FIG. 22B shows a perspective exploded view of the embodiment of theinvention shown in FIG. 22A.

FIG. 23A depicts a posterior view of the embodiment of the implant ofthe invention shown in FIG. 22A.

FIG. 23B shows a posterior view of a locking plate of the embodiment ofthe implant of the invention shown in FIG. 22A.

FIG. 24A depicts a lateral side view of the embodiment of the implant ofthe invention shown in FIG. 22A.

FIG. 24B shows a lateral side view of the keel of the locking plate ofthe embodiment of the implant of the invention shown in FIG. 22A.

FIG. 25A shows a perspective view of a further embodiment of the implantof the invention.

FIG. 25B shows a side view of the embodiment of the implant of theinvention in FIG. 25A, having a curved, uniformly-thick artificial facetjoint including a tapered end

FIG. 26A shows an anterior perspective view of a further embodiment ofthe implant of the invention.

FIG. 26B shows a posterior perspective view of the embodiment of theimplant of the invention depicted in FIG. 26A.

FIG. 27A depicts a side view of the embodiment of the implant of theinvention shown in FIGS. 26A and 26B, implanted in the cervical spine.

FIG. 27B shows a posterior view of the embodiment of the implant of theinvention shown in FIGS. 26A, 26B, and 27A, implanted in the cervicalspine.

FIG. 28A depicts a posterior perspective view of a further embodiment ofthe implant of the invention.

FIG. 28B depicts a side view of the embodiment of the implant of theinvention shown in FIG. 28A.

FIG. 29A depicts a side view of an embodiment of a sizing tool of theinvention.

FIG. 29B depicts a top view of an embodiment of the sizing tool of theinvention depicted in FIG. 29A.

FIG. 29C depicts a perspective view of an embodiment of the sizing toolof the invention depicted in FIGS. 29A-B.

FIG. 29D depicts a side view of the head of the sizing tool of theinvention depicted in FIG. 29A

FIG. 29E depicts a cross-sectional view of the head of the sizing toolof the invention depicted in FIGS. 29A-C.

FIG. 30 is a flow diagram of an embodiment of a method of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide for a minimally invasivesurgical implantation method and apparatus for cervical spine implantsthat preserves the physiology of the spine. In particular, embodimentsprovide for distracting the cervical spine to increase the foraminadimension in extension and neutral positions. Such implants distract, orincrease the space between, the vertebrae to increase the foraminal areaor dimension, and reduce pressure on the nerves and blood vessels of thecervical spine. In a specific preferred embodiment, an implantedinterfacet spacer of 1.5 mm to 2.5 mm in width can result in interfacetdistraction that increases foramina dimension in extension and neutral.Other interfacet spacer dimensions also are contemplated by theinvention described herein below. The present embodiments also preservemobility of the facet joints.

Further embodiments of the present invention accommodate the distinctanatomical structures of the spine, minimize further trauma to thespine, and obviate the need for invasive methods of surgicalimplantation. Embodiments of the present invention also address spinalconditions that are exacerbated by spinal extension.

FIG. 1 shows a simplified diagram of a portion of the cervical spine,focusing on a cervical facet joint 1 formed between two adjacentcervical vertebrae. The spinous processes 3 are located posteriorly andthe vertebral bodies 5 are located anteriorly, and a nerve root canal 7is visible.

FIG. 2 depicts cervical foraminal stenosis. From the drawing, the nerveroot canal 7 is narrowed relative to the nerve root canal 7 depicted inFIG. 1. The spinal canal and/or intervertebral foramina also can benarrowed by stenosis. The narrowing can cause compression of the spinalcord and nerve roots.

FIG. 3A shows a first embodiment 100 of the present invention, which ismeant to distract at least one facet joint, in order to increase thedimension of the neural foramen while retaining facet joint mobility.The wedge-shaped embodiment 100 is a wedge-shaped implant that can bepositioned in the cervical facet joint 101 to distract the joint andreverse narrowing of the nerve root canal 107. In this embodiment 100,the implant is positioned with the narrow portion of the wedge facinganteriorly. However, it is also within the scope of the presentinvention to position embodiment 100 (FIG. 3B) with the wide portion ofthe wedge facing anteriorly, to correct for cervical kyphosis or loss ofcervical lordosis.

It is to be understood that implants in accordance with the presentinvention, and/or portions thereof can be fabricated from somewhatflexible and/or deflectable material. In these embodiments, the implantand/or portions thereof can be made out of a polymer, such as athermoplastic. For example, in one embodiment, the implant can be madefrom polyketone, known as polyetheretherketone (“PEEK”). Still morespecifically, the implant can be made from PEEK 450G, which is anunfilled PEEK approved for medical implantation available from Victrexof Lancashire, Great Britain. Other sources of this material includeGharda located in Panoli, India. PEEK has the following approximateproperties: Property Value Density 1.3 g/cc Rockwell M 99 Rockwell R 126Tensile Strength 97 MPa Modulus of Elasticity 3.5 GPa Flexural Modulus4.1 GPa

The material specified has appropriate physical and mechanicalproperties and is suitable for carrying and spreading a physical loadbetween the adjacent spinous processes. The implant and/or portionsthereof can be formed by extrusion, injection, compression moldingand/or machining techniques.

In some embodiments, the implant can comprise, at least in part,titanium or stainless steel, or other suitable implant material which isradiopaque, and at least in part a radiolucent material that does notshow up under x-ray or other type of imaging. The physician can have aless obstructed view of the spine under imaging, than with an implantcomprising radiopaque materials entirely. However, the implant need notcomprise any radiolucent materials.

It should be noted that the material selected also can be filled. Forexample, other grades of PEEK are also available and contemplated, suchas 30% glass-filled or 30% carbon-filled, provided such materials arecleared for use in implantable devices by the FDA, or other regulatorybody. Glass-filled PEEK reduces the expansion rate and increases theflexural modulus of PEEK relative to that unfilled PEEK. The resultingproduct is known to be ideal for improved strength, stiffness, orstability. Carbon-filled PEEK is known to enhance the compressivestrength and stiffness of PEEK and to decrease its expansion rate.Carbon-filled PEEK offers wear resistance and load-carrying capability.

In this embodiment 100, the implant is manufactured from PEEK, availablefrom Victrex. As will be appreciated, other suitable similarlybiocompatible thermoplastic or thermoplastic polycondensate materialsthat resist fatigue, have good memory, are flexible, and/or deflectable,have very low moisture absorption, and good wear and/or abrasionresistance, can be used without departing from the scope of theinvention. The spacer also can be comprised of polyetherketoneketone(“PEKK”). Other material that can be used include polyetherketone(“PEK”), polyetherketoneetherketoneketone (“PEKEKK”), andpolyetheretherketoneketone (“PEEKK”), and generally apolyaryletheretherketone. Further, other polyketones can be used as wellas other thermoplastics. Reference to appropriate polymers that can beused in the implant can be made to the following documents, all of whichare incorporated herein by reference. These documents include: PCTPublication WO 02/02158 A1, dated Jan. 10, 2002, entitled“Bio-Compatible Polymeric Materials”; PCT Publication WO 02/00275 A1,dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials; and,PCT Publication WO 02/00270 A1, dated Jan. 3, 2002, entitled“Bio-Compatible Polymeric Materials.” Other materials such as Bionate®,polycarbonate urethane, available from the Polymer Technology Group,Berkeley, Calif., may also be appropriate because of the good oxidativestability, biocompatibility, mechanical strength and abrasionresistance. Other thermoplastic materials and other high molecularweight polymers can be used.

Turning now to FIG. 4, the embodiment 200 of the implant has a jointinsert 210, also herein referred to as an artificial facet joint, thatis positioned in the cervical facet joint 101. The joint insert 210 canbe wedge-shaped with the narrow part of the wedge facing anteriorly.Alternatively, the joint insert 210 need not be wedge-shaped but can beof substantially uniform thickness, the thickness determined by anindividual patient's need for distraction of the cervical facet joint201. As with embodiment 100, one objective of this embodiment is facetjoint distraction, and joint mobility after implantation. The jointinsert 210 is continuous with a posterior sheath 220 bent at an anglefrom the joint insert 210 to align substantially parallel with the bone.The posterior sheath can lie against the lamina, preferably against thelateral mass. The posterior sheath 220 can have a bore 230 which canaccept a bone screw 240. Alternatively, the bore 230 can accept anyother appropriate and/or equivalent fixation device capable of fixingthe embodiment 200 to the spine. The device is thereby affixed to thevertebra, preferably by fixing to the lateral mass.

FIG. 5 shows embodiment 300, which is the use of two embodiments 200,each fixed to one of two adjacent cervical vertebrae. As with embodiment200, the implanted facet joint is distracted and joint mobility isretained. A joint insert 310 from each of the two implants is insertedand positioned in the cervical facet joint 301. In this embodiment, thejoint inserts 310 are substantially flat and parallel to each other andare not wedge-shaped. Alternatively, the joint inserts 310 can togetherdefine a wedge-shaped insert that is appropriate for the patient. Thetwo joint inserts 310 combined can have, by way of example, the shape ofthe joint insert 210 in FIG. 4. Embodiment 300 then can be fixed to thespine with a screw 340 or any other appropriate fixation device,inserted through a bore 330 in the posterior sheath 320. The posteriorsheath 320 can be threaded to accept a screw. The screw can be embeddedin the lamina, preferably in the lateral mass, where possible.

It is within the scope of the present invention to use and/or modify theimplants of the invention to correct cervical spine kyphosis, or loss oflordosis. FIG. 6 depicts a cervical spine lordosis. FIG. 7 demonstratesan embodiment 400 which contemplates positioning two implants to correctfor this spinal abnormality while retaining facet joint mobility. Thejoint insert 410 of each implant is shaped so that it is thicker at itsanterior portion. Alternatively, the implants can be shaped to bethicker at the posterior ends, for example as depicted in FIG. 3A. Theposterior sheath 420 of each implant is bent at an angle from the jointinsert 410 to be positioned adjacent to the lateral mass and/or lamina,and has a bore 430 to accept a screw 440 or other appropriate and/orequivalent fixation means to fix the embodiment 400 to the spine,preferably to the lateral mass. The placement of two joint inserts 410in the cervical facet joint 401 distracts the facet joint, which shiftsand maintains the vertebrae into a more anatomical position to preservethe physiology of the spine.

FIG. 8 shows a further embodiment 500 of the implant of the invention,wherein the joint insert 510 has a keel 550 on an underside of the jointinsert 510. The keel 550 can be made of the same material or materialsset forth above. The surfaces of the keel 550 can be roughened in orderto promote bone ingrowth to stabilize and fix the implant 500. In otherembodiments, the keel 550 can be coated with materials that promote bonegrowth such as, for example, bone morphogenic protein (“BMP”), orstructural materials such as hyaluronic acid “HA,” or other substanceswhich promote growth of bone relative to and into the keel 550.

The keel 550 can be embedded in the facet bone, to facilitate implantretention. The keel 550 can be placed into a channel in the facet bone.The channel can be pre-cut. Teeth (not shown), preferably positionedposteriorly, also may be formed on the keel 550 for facilitatingretention of the implant 500 in the cervical facet joint 501. As notedabove, the joint insert 510 can be substantially flat or wedge-shaped,depending upon the type of distraction needed, i.e., whether distractionis also necessary to correct abnormal curvature or lack of curvature inthe cervical spine. Because the joint is not fused, mobility isretained, as with the embodiments described above and herein below.

FIG. 9 illustrates that a further embodiment 600 of the implant of theinvention can have both screw fixation and a keel 650 for stability andretention of the implant 600. On embodiment 600, the joint insert 610 iscontinuous with a posterior sheath 620 having a bore hole 630 to accepta screw 640 which passes through the bore 630 and into the bone of thevertebrae, preferably into the lateral mass, or the lamina. The bore 630can be threaded or not threaded where it is to accept a threaded screwor equivalent device. Alternatively, the bore 630 need not be threadedto accept a non-threaded equivalent device. The keel 650 is connectedwith the joint insert 610 and embeds in the bone of the cervical facetjoint 601 to promote implant retention.

A further alternative embodiment 700 is illustrated in FIG. 10. In thisembodiment 700, the joint insert 710 has on a lower side at least onetooth 760. It should be clear to one of ordinary skill in the art that aplurality of teeth 760 is preferable. The teeth 760 are able to embed inthe bone of the cervical facet joint 701 to facilitate retention of theimplant 700 in the joint 701. The teeth 760 can face in a directionsubstantially opposite the direction of insertion, for retention of theimplant 700. As above, the joint insert 710 can be wedge-shaped orsubstantially even in thickness, depending upon the desired distraction.Because the implant distracts and is retained without fusion, facetjoint mobility is retained.

FIG. 11 depicts a further embodiment 800 of the implant of theinvention. In this embodiment 800, the joint insert 810 is continuouswith a posterior sheath 820 having a bore 830 for accepting a fixationdevice 840, as described above. The fixation device 840 can be a screwwhich fits into a threaded bore 830; alternatively, the fixation device830 can be any other compatible and appropriate device. This embodiment800 further combines at least one tooth 860 on an underside of the jointinsert 810 with the posterior sheath 820, bore 830 and fixation device840 to address fixation of the implant 800 in a cervical facet joint801. It will be recognized by one of ordinary skill in the art that theimplant 800 can have a plurality of teeth 860 on the underside of thejoint insert 810.

FIG. 12 shows yet another embodiment 900 of an implant of the presentinvention. In this embodiment 900, the joint inserts 910 of two implants900 are positioned in a cervical facet joint 901. As described above,the joint inserts 910 can be wedge-shaped as needed to restoreanatomical curvature of the cervical spine and to distract, or the jointinserts 910 can be of substantially uniform thickness. The implants 900each comprise a joint insert 910 with an outer surface 970 thatinteracts with the bone of the cervical facet joint 901. On the upperimplant 900, the surface 970 that interacts with the bone is the uppersurface 970 and on the lower implant 900, the surface 970 that interactswith the bone is the lower surface 970. Each surface 970 can comprise abone ingrowth surface 980 to create a porous surface and thereby promotebone ingrowth and fixation. One such treatment can be with plasma spraytitanium, and another, with a coating of sintered beads. Alternatively,the implant 900 can have casted porous surfaces 970, where the poroussurface is integral to the implant 900. As a further alternative, thesurfaces 970 can be roughened in order to promote bone ingrowth intothese defined surfaces of the implants 900. In other embodiments, thesurfaces 970 can be coated with materials that promote bone growth suchas for example bone morphogenic protein (“BMP”), or structural materialssuch as hyaluronic acid (“HA”), or other substances which promote growthof bone on other external surfaces 970 of the implant 900. Thesemeasures facilitate fixation of the implants 900 in the facet joint, butdo not result in fusion of the joint, thereby retaining facet jointmobility, while also accomplishing distraction of the joint.

FIG. 13 depicts yet another embodiment 1000 of the implant of thepresent invention. In this embodiment 1000, the joint inserts 1010 oftwo implants 1000 are positioned in a cervical facet joint 1001. Asdescribed above, the joint inserts 1010 can be wedge-shaped as needed torestore anatomical curvature of the cervical spine and to distract, orthe joint inserts 1010 can be of substantially uniform thickness. Theimplants 1000 each comprise a joint insert 1010 with an outer surface1070 that interacts with the bone of the cervical facet joint 1001. Onthe upper implant 1000, the surface 1070 that interacts with the bone isthe upper surface and on the lower implant 1000, the surface 1070 thatinteracts with the bone is the lower surface. As set forth above, eachouter surface 1070 can comprise a bone ingrowth surface 1080 to create aporous surface and thereby promote bone ingrowth and fixation, withoutfacet joint fusion and loss of mobility. In one preferred embodiment,the bone ingrowth surface 1080 can be created with plasma spraytitanium, and/or with a coating of sintered beads. In an alternativepreferred embodiment, the implant 1000 can have casted porous surfaces1070, where the porous surface is integral to the implant 1000. In afurther alternative preferred embodiment, the surfaces 1070 can beroughened in order to promote bone ingrowth into these defined surfacesof the implants 1000. In other preferred embodiments, the surfaces 1070can be coated with materials that promote bone growth such as forexample BMP, or structural materials such as HA, or other substanceswhich promote growth of bone on other external surfaces 1070 of theimplant 1000.

The implant 1000 can have a posterior alignment guide 1090. Theposterior alignment guides 1090 of each implant 1000 can be continuouswith the joint inserts 1010. The posterior alignment guidessubstantially conform to the bone of the vertebrae when the jointinserts 1010 are inserted into the cervical facet joint 1001. Theposterior alignment guides 1090 are used to align the implants 1000 sothat the joint inserts 1010 contact each other and not the bones of thecervical facet joint 1001 when the joint inserts 1010 are positioned inthe cervical facet joint 1001.

FIG. 14 depicts a further embodiment 1100 of the implant of the presentinvention. In this embodiment 1100, the joint inserts 1110 of twoimplants 1100 are inserted into the cervical facet joint 1101. Each ofthe joint inserts 1110 is continuous with a cervical facet jointextender or facet-extending surface 1192. The bone contacting surfaces1170 of the joint inserts 1110 are continuous with, and at an angle to,the bone contacting surfaces 1193 of the cervical facet joint extenders1192, so that the cervical facet joint extenders 1192 conform to thebones of the vertebrae exterior to the cervical facet joint 1101. Theconformity of the cervical facet joint extenders 1192 is achieved forexample by forming the cervical facet joint extenders 1192 so that whenthe join inserts 1110 are positioned, the cervical facet joint extenders1192 curve around the bone outsider the cervical facet joint 1101.

The cervical facet joint extenders have a second surface 1184 that iscontinuous with the joint articular surfaces 1182 of the joint inserts1110. The second surfaces 1184 extend the implant 1100 posteriorly toexpand the joint articular surfaces 1182 and thereby to increase contactand stability of the spine at least in the region of the implants 1100.It is to be understood that such facet joint extenders 1192 can be addedto the other embodiments of the invention described and depicted herein.

The embodiment depicted in FIG. 15 shows two implants 1200 positioned ina cervical facet joint 1201, having bony ingrowth surfaces as onepreferred method of fixation, and using screws as another preferredmethod of fixation. In this embodiment, each of two implants 1200 has ajoint insert 1210 positioned in a cervical facet joint 1201. Asdescribed above, the joint inserts 1210 can be wedge-shaped as needed torestore anatomical curvature of the cervical spine and to distract, orthe joint inserts 1210 can be of substantially uniform thickness. Theimplants 1200 each comprise a joint insert 1210 with an outer surface1270 that interacts with the bone of the cervical facet joint 1001. Onthe upper implant 1200, the surface 1270 that interacts with the bone isthe upper surface and on the lower implant 1200, the surface 1270 thatinteracts with the bone is the lower surface. As set forth above, eachouter surface 1270 can comprise a bone ingrowth surface 1280 to create aporous surface and thereby promote bone ingrowth and fixation. In onepreferred embodiment, the bone ingrowth surface 1280 can be created withplasma spray titanium, and/or with a coating of sintered beads. In analternative preferred embodiment, the implant 1200 can have castedporous surfaces 1270, where the porous surface is integral to theimplant 1200. In a further alternative embodiment, the surfaces 1270 canbe roughened in order to promote bone ingrowth into these definedsurfaces of the implants 1200. In other preferred embodiments, thesurfaces 1270 can be coated with materials that promote bone growth suchas for example BMP, or structural materials such as HA, or othersubstances which promote growth of bone on other external surfaces 1270of the implant 1200.

Screw fixation or other appropriate fixation also can be used withimplants 1200 for fixation in the cervical facet joint 1201. The jointinsert 1210 is continuous with a posterior sheath l220 bent at an anglefrom the joint insert 1210 to align substantially parallel with thebone, preferably the lateral mass or lamina. The posterior sheath 1220can have a bore 1230 which can accept a bone screw 1240, preferably intothe lateral mass or lamina. Alternatively, the bore 1230 can accept anyother appropriate and/or equivalent fixation means for fixing theembodiment 1200 to the spine.

FIG. 16 depicts a further preferred embodiment of the present invention.In this embodiment 1300, two joint inserts 1310 are positioned in thecervical facet joint 1301. The joint inserts each have outer surfaces1370 that interact with the bone of the vertebrae forming the cervicalfacet joint. These outer surfaces 1370 of the embodiment 1300 can betreated to become bone ingrowth surfaces 1380, which bone ingrowthsurfaces 1380 contribute to stabilizing the two joint inserts 1310 ofthe implant 1300. In one preferred embodiment, the bone ingrowth surface1380 can be created with plasma spray titanium, and/or with a coating ofsintered beads. In an alternative preferred embodiment, the implant 1300can have casted porous surfaces 1370, where the porous surface isintegral to the implant 1300. In a further alternative embodiment, thesurfaces 1370 can be roughened in order to promote bone ingrowth intothese defined surfaces of the implants 1300. In other preferredembodiments, the surfaces 1370 can be coated with materials that promotebone growth such as for example BMP, or structural materials such as HA,or other substances which promote growth of bone on other externalsurfaces 1370 of the implant 1300. This fixation stabilizes the implant1300 in the facet joint without fusing the joint, and thus the implantpreserves joint mobility, while accomplishing distraction and increasingforaminal dimension.

Also shown in FIG. 16 are articular inner surfaces 1382 of the implants1300. These surfaces can be formed from a metal and polyethylene, thematerial allowing flexibility and providing for forward bending/flexionand backward extension of the cervical spine. The embodiment 1300 ofFIG. 16 can be made in at least two configurations. The firstconfiguration includes a flexible spacer 1382 made, by way of example,using polyethylene or other suitable, flexible implant material. Theflexible spacer 1382 can be permanently affixed to the upper and lowerjoint insert 1310. The spacer 1382 can be flat or wedge-shaped or haveany other shape that would correct the curvature of the spine. In otherconfigurations, the spacer 1382 can be affixed to only the upper insert1310 or to only the lower insert 1310. Alternatively, a spacer 1382 canbe affixed to each of an upper insert 1310 and a lower insert 1310 withthe upper insert 1310 and the lower insert 1310 being separate units.

FIG. 17 shows a further preferred embodiment of the implant of thepresent invention. In this embodiment 1400, the implant has a roller1496 mounted on a joint insert 1410, the roller being a further means ofpreserving joint mobility while accomplishing distraction. Both theroller 1496 and the joint insert 1410 are positioned in the cervicalfacet joint 1401. The joint insert 1410 as in other embodiments has abone-facing surface 1470 and joint articular surface 1482. Thebone-facing surface 1470 can interact with the lower bone of thecervical facet joint 1401. Alternatively, the bone-facing surface caninteract with the upper bone of the cervical facet joint 1401. Betweenthe bone-facing surface 1470 and the joint articular surface 1482 is anaxis about which the roller 1496 can rotate. The roller 1496 rotates ina cavity in the joint insert 1410, and interacts with the top bone ofthe cervical facet joint 1401. Alternatively, where the bone-facingsurface 1470 of the joint insert 1410 interacts with the top bone of thecervical facet joint 1401, the roller 1496 rotates in a cavity in thejoint insert 1410 and interacts with the lower bone of the cervicalfacet joint 1401. The rotation of the roller 1496 allows flexion andextension of the cervical spine. Alternatively, a roller such as roller1496 can be secured to an upper and a lower insert such as inserts 410in FIG. 7. As depicted in FIG. 18, a plurality of rollers 1496 also ispossible.

FIG. 19 depicts a further embodiment of the implant of the presentinvention. In this embodiment, two implants 1500 are implanted in thecervical facet joint 1501. Screw fixation or other appropriate fixationis used with implants 1500 for fixation in the cervical facet joint1501. The joint insert 1510 is continuous with a posterior sheath 1520bent at an angle from the joint insert 1510 to align substantiallyparallel with the bone, preferably the lateral mass or lamina. Theposterior sheath 1520 of each implant 1500 can have a bore 1530 whichcan accept a bone screw 1540, preferably into the lateral mass orlamina. Alternatively, the bore 1530 can accept any other appropriateand/or equivalent fixation means for fixing the embodiment 1500 to thespine. The head of the screw 1540 in each posterior sheath 1520 of eachimplant 1500 has a groove 1598 or other mechanism for retaining anelastic band 1597. The elastic band 1597 is looped around each of thetwo screws 1540 to restrain movement of the cervical spine withouteliminating facet joint mobility. The band 1597 preferably can restrainflexion and lateral movement. The elastic band 1597 can be made of abiocompatible, flexible material.

FIG. 20 shows an alternative to use of an elastic band as in FIG. 19. Inthe embodiment in FIG. 20, the elastic band is replaced with a springrestraint 1699, which extends between the heads of two screws 1640, onescrew fixing each of two implants 1600 in the cervical facet joint 1601.

FIG. 21 shows another alternative to using an elastic band and/or aspring as in FIG. 19 or 20. In FIG. 21, magnets 1795 is used forrestraint between the two screws 1740. The magnet 1795 can either becomprised of two opposing magnetic fields or two of the same magneticfields to operate to restrain movement. The head of one of the twoscrews 1740 is magnetized, and the head of the other screw 1740 ismagnetized with either the same or opposite field. If the magnets 1795have the same polarity, the magnets 1795 repel each other and thus limitextension. If the magnets 1795 have opposite polarities, the magnets1795 attract each other and thus limit flexion and lateral movement.

FIGS. 22A-24B, depict a further embodiment 1800 of the implant of thepresent invention. In this embodiment, an artificial facet joint 1810 isconnected with a lateral mass plate 1820 with a hinge 1822. The hinge1822 allows the lateral mass plate 1820 to bend at a wide range ofangles relative to the artificial facet joint and preferably at an angleof more than 90 degrees, and this flexibility facilitates positioningand insertion of the artificial facet joint 1810 into a patient's facetjoint, the anatomy of which can be highly variable among individuals.This characteristic also applies to embodiments described below, whichhave a hinge or which are otherwise enabled to bend by some equivalentstructure or material property. The hinge 1822 further facilitatescustomizing the anchoring of the implant, i.e., the positioning of afixation device. The hinge enables positioning of the lateral mass plate1820 to conform to a patient's cervical spinal anatomy, and the lateralmass plate 1820 accepts a fixation device to penetrate the bone. Theartificial facet joint 1810 can be curved or rounded at a distal end1812 (FIG. 23A), and convex or dome-shaped on a superior surface 1813 toapproximate the shape of the bone inside the facet joint. The inferiorsurface 1815 can be flat or planar. Alternatively, the inferior surface1815 can be concave. As another alternative, the inferior surface 1815can be convex.

The lateral mass plate 1820, when implanted in the spine, is positionedoutside the facet joint, preferably against the lateral mass or againstthe lamina. The lateral mass plate 1820 has a bore 1830 therethrough.The bore 1830 can accept a bone screw 1840, also referred to as alateral mass screw, to secure the lateral mass plate 1820 preferably tothe lateral mass or alternatively to another part of the spine, and thusto anchor the implant. The lateral mass screw 1840 preferably has ahexagonal head to accept an appropriately-shaped wrench. As describedbelow, the head accepts a compatible probe 1826 from a locking plate1824.

The locking plate 1824 includes a keel 1828 with a wedge shaped distalend to anchor the implant, preferably in the lateral mass or in thelamina, outside the facet joint and to prevent rotation of the lateralmass plate 1820 and the locking plate 1824. The keel 1828 aligns with agroove 1823 through an edge of the lateral mass plate 1820 to guide andalign the keel 1828 as the keel 1828 cuts into a vertebra.

As noted above, the locking plate 1824 includes a probe 1826 that fitsagainst the head of the lateral mass screw 1840. The locking platefurther includes a bore 1831 that can accept a machine screw (not shown)which passes through to an aligned bore 1829 in the lateral mass plate1820 to hold the locking plate 1824 and the lateral mass plate 1820together without rotational displacement relative to each other. Thelocking plate 1824 thus serves at least two functions: (1) maintainingthe position of the lateral mass screw 1840 with the probe 1826, so thatthe screw 1840 does not back out; and (2) preventing rotation of theimplant with the keel 1828 and machine screw relative to the cervicalvertebra or other vertebrae.

It is to be understood that other mechanisms can be used to lock thelocking plate 1824 to the lateral mass plate 1820. For example, thelocking plate can include a probe with barbs that can be inserted into aport in the lateral mass plate. The barbs can become engaged in ribsthat define the side walls of the port in the lateral mass plate

In the preferred embodiment depicted in FIGS. 25A, 25B, the lateral massplate 1920 includes a recessed area 1922 for receiving the locking plate1924 so that the locking plate 1924 is flush with the upper surface 1925of the lateral mass plate 1920 when the probe 1926 is urged against thelateral mass screw 1940 and the keel 1928 is inserted into the lateralmass or the lamina of the vertebra. In the preferred embodiment depictedin FIGS. 25A, 25B, the shape and contours of the artificial facet joint1910 can facilitate insertion of the artificial facet joint 1910 intothe cervical facet joint. In this embodiment, the artificial facet joint1910 has a rounded distal end 1912. The distal end 1912 is tapered inthickness to facilitate insertion. The tapered distal end 1912 meets andis continuous with a proximal mid-section 1916 which, in this preferredembodiment, has a uniform thickness, and is connected flexibly,preferably with a hinge 1922, to the lateral mass plate 1920, asdescribed above. The artificial facet joint 1910, with its proximalmid-section 1916 and tapered distal end 1912, is curved downward,causing a superior surface 1913 of the artificial facet joint 1910 to becurved. The curve can cause the superior surface 1913 to be convex, andthe convexity can vary among different implants 1900 to suit theanatomical structure of the cervical facet joint(s) of a patient. Aninferior surface 1915 accordingly can be preferably concave, flat, orconvex. The curved shape of the implant can fit the shape of a cervicalfacet joint, which is comprised of an inferior facet of an uppervertebra and a superior facet of a lower adjacent vertebra. The convexshape of the superior surface 1913 of the artificial facet joint 1910fits with a concave shape of the inferior facet of the upper cervicalvertebrae. The concave shape of the inferior surface 1915 of theartificial facet joint 1910 fits with the convex shape of the superiorfacet of the cervical vertebrae. The degree of convexity and concavityof the artificial facet joint inferior and superior surfaces can bevaried to fit a patient's anatomy and the particular pairing of adjacentcervical vertebrae to be treated. For example, a less-curved artificialfacet joint 1910 can be used where the patient's cervical spinal anatomyis sized (as described below) and found to have less convexity andconcavity of the articular facets. Generally for the same level theinput for the right and left facet joint will be similarly shaped. It isexpected that the similarity of shape of the artificial facet joint andthe smooth, flush surfaces will allow distraction of the facet jointwithout loss of mobility or damage to the bones of the cervical spine.Further, and preferably, the width of the mid-section 1916 is from 1.5mm to 2.5 mm.

Except as otherwise noted above, the embodiment shown in FIGS. 22A-24Bis similar to the embodiment shown in FIGS. 25A, 25B. Accordingly theremaining elements on the 1900 series of element numbers is preferablysubstantially similar to the described elements in the 1800 series ofelement numbers, as set forth above. Thus, by way of example, elements1923, 1928, 1929 and 1930 are similar, respective elements 1823, 1828,1829 and 1830.

FIG. 30 is a flow chart of the method of insertion of an implant of theinvention. The embodiment 1800 or 1900 of the present inventionpreferably is inserted in the following manner (only elements of theembodiment 1800 will be set forth herein, for purposes of the writtendescription of a method of the invention). First the facet joint isaccessed. A sizing tool 2200 (see FIGS. 29A-C) can be inserted to selectthe appropriate size of an implant of the invention for positioning inthe cervical facet joint. This step may be repeated as necessary with,if desired, different sizes of the tool 2200 until the appropriate sizeis determined. This sizing step also distracts the facet joint andsurrounding tissue in order to facilitate insertion of the implant.Then, the artificial facet joint 1810 is urged between the facets intothe facet joint. The facet itself is somewhat shaped like a ball andsocket joint. Accordingly, in order to accommodate this shape, theartificial joint 1810 can have a rounded leading edge shaped like awedge or tissue expander to cause distraction of the facet joint as theartificial facet joint is urged into the facet joint of the spine. Theartificial facet joint 1810 also includes the convex surface 1813 inorder to more fully accommodate the shape of the facet joint of thespine. However, as set forth above and as depicted in FIG. 25B, it ispossible in the alternative to have a curve-shaped artificial facetjoint 1910 with a convex superior surface 1913 and a concave inferiorsurface 1915, the distal end 1912 tapering to facilitate insertion,while the remainder of the artificial facet joint 1910, (i.e., theproximal section 1916) has a uniform thickness.

Once the artificial joint 1810 is positioned, the lateral mass plate1820 is pivoted downward about the hinge 1822 adjacent to the vertebraeand preferably to the lateral mass or to the lamina. Thus the lateralmass plate 1820 maybe disposed at an angle relative to the artificialfacet joint 1810 for a representative spine configuration. It is to beunderstood that as this embodiment is hinged the final position of thelateral mass plate 1820 relative to the artificial facet joint 1800 willdepend on the actual spine configuration. It is to be understood thatembodiments of the invention can be made without a hinge, as long as theconnection between the artificial facet joint and the lateral mass plateis flexible enough to allow the lateral mass plate to be bent relativeto the artificial facet joint in order to fit the anatomy of thepatient. Once the lateral mass plate 1820 is positioned, or prior to thepositioning of the lateral mass plate 1820, a bore can be drilled in thebone to accommodate the bone screw 1824. Alternatively the screw 1824can be self-tapping. The screw is then placed through the bore 1830 andsecured to the bone, preferably the lateral mass or the lamina, therebyholding the artificial facet joint 1800 in place. In order to lock thebone screw 1824 in place and to lock the position of the artificialfacet joint 1800 and the lateral mass plate 1820 in place, the lockingplate 1824 is positioned over the lateral mass plate 1820. Sopositioned, the probe 1826 is positioned through the bore 1830 andagainst the head of the bone screw to keep the bone screw from moving.The keel 1828, having a sharp chisel-shaped end, preferably can self-cuta groove in the bone so that the keel 1828 is locked into the bone asthe keel 1828 is aligned by, and received in, a groove 1831 of thelateral mass plate 1820. Alternatively, a groove can be pre-cut in thebone to receive the keel 1828. As this occurs the bore 1829 of thelocking plate 1824 aligns with the threaded bore 1831 of the lateralmass plate 1820 and a machine screw can be inserted to lock the lockingplate relative to the lateral mass plate. This locking prevents thelateral mass plate 1820 and the artificial facet joint 1810 fromrotating and, as previously indicated, prevents the bone screw 1840 frombacking out from the vertebra. Preferably the implant is between the C5and C6 vertebrae level, or the C6 and C7 vertebrae level. It is notedthat two implants preferably will be implanted at each level betweenvertebrae. That is, an implant 1800 will be placed in a right facetjoint and also in a left facet joint when viewed from a posterior viewpoint. This procedure can be used to increase or distract the foraminalarea or dimension of the spine in an extension or in neutral position(without having a deleterious effect on cervical lordosis) and reducethe pressure on the nerves and blood vessels. At the same time thisprocedure preserves mobility of the facet joint.

FIGS. 26A-27B show a further embodiment of the implant of the invention,with the embodiment 2000 implanted in the cervical spine as depicted inFIGS. 27A and 27B. The implant 2000 comprises a first artificial facetjoint 2010 and a second artificial facet joint 2010. Each artificialfacet joint can have a distal end 2012 that is tapered or wedge-shapedin a way that facilitates insertion into the cervical facet joints onboth sides of two adjacent cervical vertebrae at the same level. Theartificial facet joints further can be dome-shaped, or convex on asuperior surface 2013, to approximate the shape of the cervical facetsof the cervical facet joints.

The first and second artificial facet joints 2010 are bridged togetherby a collar 2015. The collar 2015 passes between the spinous processesof the adjacent cervical vertebrae. As can be seen in FIG. 26B, theimplant can preferably be “V” shaped or “boomerang” shaped. The entireimplant 2000 or the collar 2015 of the implant can be made of a flexiblematerial such as titanium, so that it is possible to bend the collar2015 so that it conforms preferably to the shape of the lateral mass orthe lamina of the cervical vertebrae of the patient and thereby holdsthe implant in place with the artificial facet joints 2010 inserted inthe cervical facet joints. Bores 2029 are preferably are providedthrough implant 2000 adjacent to the artificial facet joint 2010respectively. These bores 2029 can receive bone screws to position theimplant 2000 against the lateral mass or the lamina as shown in FIGS.27A, 27B. The description of the embodiment 2100, in FIGS. 28A, 28Bprovide further details concerning the method of affixing the implant2000 to the vertebrae. The implant 2100 also can be made of PEEK orother materials as described herein. Embodiment 2000 (the “boomerang”shape depicted in FIG. 27B) further can have a locking plate as, forexample, the locking plate 1824 in FIG. 22A. The locking plate forembodiment 2000 (not shown) can have the same features as locking plate1824, that is: (1) a probe 1826 that interacts with the bone screws toprevent the bone screws from backing out of the bone, the likelyconsequence of which would be displacement of the implant 2000; and (2)a keel 1828 with a chisel end to embed in the bone and thus to preventrotational displacement of the implant. However, given the collar 2015configuration of embodiment 2000, a chisel may not serve the samepurpose as with the embodiments set forth above, which lack a collarstabilized by two bone screws. Therefore, a locking plate on embodiment2000 can be provided without a keel.

FIGS. 28A and 28B depict a further embodiment of the implant of theinvention 2100. In this embodiment 2100, the collar 2115 can be made ofa flexible material such as titanium, of a substantially inflexiblematerial, or of other materials described herein. Substantialflexibility can also be derived from connecting a first artificial facetjoint 2110 with the collar 2115 using a first hinge 2117, and connectinga second artificial facet joint 2110 with the collar 2115 using a secondhinge 2117. Using the first hinge 2117 and the second hinge 2117, thecollar 2115 can be pivoted downward to conform to a particular patient'scervical spinal anatomy. In other words, the degree of pivoting willvary among different patients, and the first hinge 2117 and second hinge2117 allow the implant 2100 to accommodate the variance.

In the hinged embodiment 2100, and similar to the embodiment 2000, thecollar 2115 can have a first bore 2129 inferior to the first hinge 2117,and a second bore 2129 inferior to the second hinge 2117. A first bonescrew penetrates the first bore 2130 and into the lateral mass or thelamina, and the second bone screw penetrates the second bore 2130 andinto the lateral mass or the lamina, the first and second bone screwsserving to anchor the implant. A bore, preferably in the lateral mass,can be drilled for the first bone screw and for the second bone screw.Alternatively, the bone screws can be self-tapping. A first lockingplate similar to the plate 1924 (FIG. 25A) can be secured about the headof the first bone screw and a second locking plate can be secured aboutthe head of the second bone screw to prevent displacement of the firstand second bone screws 2140. The first locking plate can block the firstbone screw with a probe and the second locking plate can block to thesecond bone screw with a probe.

It should be noted that embodiments 2000 and 2100 also can be configuredfor accommodating treatment of cervical spinal stenosis and othercervical spine ailments where only a single cervical facet joint betweenadjacent vertebrae requires an implant, i.e., where treatment is limitedto one lateral facet joint. In that case, the collar 2015, 2115 extendsmedially without extending further to join a second artificial facetjoint 2010, 2110. For the hinged embodiment 2100, the implant comprisesa single hinge 2117, and the collar 2115 has only one bore 2129 toaccept one bone screw to secure the implant 2100.

FIGS. 29A-E, depict a sizing and distracting tool 2200 of the invention.Sizing tool 2200 has a handle 2203 and a distal head 2210 that is shapedas an artificial facet joint (e.g., 1810) of an implant of theinvention. That is, the head 2210 preferably will have essentially thesame features as the artificial facet joint 1810, but the dimensions ofthe head 2210 will vary from one tool 2200 to the next, in order to beable to use different versions of the sizing tool 2200 to determine thedimensions of the cervical facet joint that is to be treated and then toselect an appropriately-sized implant. The head 2210 preferably can beused to distract the facet joint prior to the step of implanting theimplant in the facet joint. In this regard, the head 2210 is rounded atthe most distal point 2212, and can be a tapered to facilitate insertioninto a cervical facet joint. The head 2210 also can have a slightlyconvex superior surface 2213, the degree of convexity varying amongdifferent sizing tools 2200 in order to determine the desired degree ofconvexity of an implant to be implanted in the cervical facet joint. Thehead 2210 may have a uniform thickness along a proximal mid-section2216. Accordingly, the inferior surface 2215 preferably can be concave.Alternatively, the proximal mid-section 2212 may be convex on thesuperior surface 1813 without being uniform in thickness. Thus, theinferior surface 2215 can be flat or planar. The head also can becurved.

The head 2210 has a stop 2218 to prevent over-insertion of the head 2210of the sizing tool 2200 into the facet joint. The stop 2218 can be aridge that separates the head 2210 from the handle 2203. Alternatively,the stop 2218 can be any structure that prevents insertion beyond thestop 2218, including pegs, teeth, and the like.

Different sizing tools 2200 covering a range of dimensions of the head2210 can be inserted successively into a cervical facet joint to selectthe appropriate size of an implant to position in the cervical spine,with the appropriate convexity and concavity of artificial facet joint.Each preferably larger head also can be used to distract the facetjoint.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.Many modifications and variations will be apparent to practitionersskilled in this art. The embodiments were chosen and described in orderto explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the following claims and theirequivalents.

1. A facet joint implant adapted to correct spinal stenosis and otherailments of the spine without eliminating mobility of the facet joint,the implant comprising: an artificial facet joint adapted to bepositioned in a spinal facet joint and to distract the spinal facetjoint, wherein the distraction causes an increase in foraminaldimension, the artificial facet joint having a connection with a firstplate; said first plate adapted to be anchored to a vertebra; and asecond plate that fastens to the first plate, the second plate having akeel adapted to penetrate the vertebra, wherein the penetration of thevertebra by the keel prevents the first plate and the second plate fromrotating.
 2. The facet joint implant as in claim 1 wherein saidconnection includes a hinge.
 3. The facet joint implant as in claim 1wherein the first plate further comprises a first bore, the first boreand a first screw accepted through said first bore to anchor the implantto a vertebra.
 4. The facet joint implant as in claim 3 furthercomprising: a second bore through the first plate; a third bore throughthe second plate that aligns with second bore on the first plate whenthe keel is implanted in the vertebra and the second plate and the firstplate are positioned to be fastened together; and a second screwaccepted through the aligned second bore and third bore, the secondscrew to fasten the first plate with the second plate and preventrotation of the first plate and the second plate relative to each other.5. The facet joint implant as in claim 3 wherein the second platefurther comprises a block, said block to interfere with movement of thefirst screw with the first plate and the second plate positionedadjacent to each other.
 6. The facet joint implant as in claim 1 whereinthe artificial facet joint is tapered so as to be adapted to causedistraction of the facet joint as the artificial facet joint is urgedinto the facet joint.
 7. The facet joint implant as in claim 1 whereinthe artificial facet joint is convex on a surface in order to be adaptedto accommodate the shape of a cervical facet joint.
 8. The facet jointimplant as in claim 1 wherein the artificial facet joint is disposableat an angle greater than 90 degrees relative to the first plate.
 9. Thefacet joint implant as in claim 1 wherein the connection between theartificial facet joint and the first plate is flexible.
 10. The facetjoint implant as in claim 1 wherein the keel includes an edge and isadapted to self-cut a groove in the lateral mass.
 11. The cervical facetjoint implant as in claim 1 wherein the implant does not requireresection of any bone.
 12. A cervical facet joint implant adapted tocorrect cervical spinal stenosis and other ailments of the cervicalspine, the implant comprising: an artificial facet joint adapted to beinserted into and to distract a cervical facet joint, wherein thedistraction increases the foraminal dimension without eliminatingmobility of the cervical facet joint; a hinge connecting the artificialfacet joint with a lateral mass plate; the lateral mass plate adapted tobe positioned against the lateral mass of the vertebra, the lateral massplate having a first bore and a second bore; a bone screw accepted bythe first bore and adapted to penetrate the lateral mass to anchor theimplant, the bone screw having a head; a locking plate that mates withthe lateral mass plate to prevent rotation of the lateral mass plate,the locking plate further comprising: a keel, said keel adapted topenetrate the vertebra and anchor the implant to the vertebra; and athird bore that aligns with the second bore, and wherein the second andthird bores accept a second screw therethrough to join the lateral massplate and the locking plate.
 13. The cervical facet joint implant as inclaim 12 wherein the second plate further comprises a block that blocksthe bone screw positioned in the artificial facet joint, with thelateral mass plate and the locking plate positioned adjacent each other.14. The cervical facet joint implant as in claim 12 including a firstsaid implant is adapted to be positioned in a first lateral cervicalfacet joint formed by two adjacent vertebrae, and a second said implantis adapted to be positioned in a second lateral facet joint formed bythe two adjacent vertebrae.
 15. The cervical facet joint implant as inclaim 12 wherein the keel has a chisel-shaped end for self-cutting agroove in the vertebra.
 16. The cervical facet joint implant as in claim12 wherein the lateral mass plate further comprises a groove thataccepts the keel of the locking plate, said groove adapted to guide thekeel as the keel cuts into the vertebra.
 17. The cervical facet jointimplant as in claim 12 wherein the artificial facet joint has a tapereddistal end, the tapered distal end to facilitate insertion.
 18. Thecervical facet joint implant as in claim 12 wherein the artificial facetjoint has a convex surface to approximate the shape of the cervicalfacet joint.
 19. A facet joint implant adapted to increase foraminaldimension in the spine comprising: an artificial facet joint adapted tobe positioned in a spinal facet joint, the artificial facet joint havinga flexible connection with a first plate; and said first plate adaptedto be anchored to the spine.
 20. The implant of claim 19 wherein saidflexible connection includes a hinge.
 21. The implant of claim 19wherein said artificial facet joint is shaped to accommodate and fitbetween superior and inferior portions of a cervical facet joint. 22.The implant of claim 19 wherein the first plate anchors to the lateralmass.
 23. The implant of claim 19 wherein the artificial facet jointdistracts the spinal facet joint and allows mobility of the spinal facetjoint.
 24. The implant of claim 19 including said artificial facet jointhaving a convex surface adapted to mate with the facet joint.
 25. Theimplant of claim 19 wherein: the artificial facet joint includes awedge-shaped front end adapted to allow the front end to be wedged intoa facet joint, wherein the artificial facet joint distracts the facetjoint and increases the foraminal area, without eliminating mobility ofthe facet joint.
 26. The implant of claim 1 wherein said second plate isreceived in a recess of said first plate such that the second plate isflush with the first plate.